Both antigen dependent and independent processes are thought to contribute to progressive renal allograft failure through pathways which may inter- relate synergistically. The overall objectives of this proposal are: to define the respective contributions of antigen-dependent and antigen- independent injury processes to chronic rejection and their mechanisms of interaction; to dissect out key factors in the pathogenesis of graft injury using specific inhibitors as probes. Project 1 is built upon the insights gained from our studies of an established rat model of chronic rejection where bilaterally nephrectomized Lewis hosts are sustained for prolonged periods by a single Fisher 344 renal allograft (F344->LEW). In the 2 wks after engraftment, well defined forms of antigen dependent and independent injuries occur which stimulate macrophage (mo) chemotaxis. MO have been implicated as effectors of chronic allograft rejection but may also play a role in antigen independent modes of renal injury. TGFbeta an established mediator of renal fibrosis and a MO product is abundantly expressed in both F344- >LEW and forerunners of antigen-independent injury resulting from nephron loss, also precede chronic injury in allografts. Remarkably, supplying additional nephron mass at the time of transplantation limits compensatory adaptive changes in allograft physiology and prevents progressive injury as effectively as sustained immunosuppression. We conclude that chronic antigen dependent and independent injuries are distinct forms of injury which operate synergistically in part because they utilize closely inter- related mechanisms. Accordingly, we will examine the pathophysiology of chronic rejection by integrating key functional, cellular and molecular changes occurring over time. The experimental results will be correlated to events occurring clinically.